The present invention relates generally to clothing for thermal regulation of the human body, and more particularly, to a self-contained thermal distribution and regulation device for cold weather apparel.
The need to maintain body temperature exists where human activities are conducted in extreme temperature environments. Very cold environments are often encountered by individuals who pursue outdoor winter activities such as snowmobilers, motorcycle riders, hunters, snow skiers, and workers, such as construction and highway workers, who work outside during the winter. Also, individuals who work in more pedestrian cold environments, such as refrigerated containers are exposed to extreme cold temperatures.
The most prevalent method today for individuals who are exposed to extreme cold temperatures or pursue outdoor winter activities to maintain their body temperature is to wear several layers of clothing, commonly referred to as “layered clothing” or “layering”. Wearing several layers of clothing on top of each other, lowers heat losses to match the body's internal heat production and protect from environmental elements. Some of the layers have different, largely non-overlapping, functions. Using more or fewer layers, or replacing one layer but not others, allows for flexible clothing to match the needs of each situation. For example, two thin layers can be warmer yet lighter than one thick layer, because the air trapped between layers serves as “thermal insulation”.
Layering typically consists of about three layers of clothing that are identified as the inner or base layer, the mid or insulating layer, and the shell or outer layer. The base layer is typically against the wearer's skin to manage moisture and keep the wearer's skin dry. The outer layer protects the wearer from environmental conditions such as wind, rain, and snow and also serves as protection over the base and insulating layers. The insulating layer provides warmth to the wearer and may be considered the most important layer worn.
The insulating layer is what keeps the wearer warm while they participate in activities in the cold. Materials used for the insulating layer vary widely; from materials used for over a century, such as wool and down, to cutting edge fleece and polypropylene and polyester materials. Additionally, the insulating layer is thick as compared to the other layers, to reduce conductive heat loss. However, heat flow is an inevitable consequence of contact between objects of differing temperature, and thus over time the wearer's clothing may not sufficiently match their body's internal heat production and they may get cold.
An effort to improve the insulating layer's ability to lower heat losses to match the body's internal heat production is realized in so-called “heated clothing” or “heated thermal clothing”. In one example, an item of heated clothing such as a vest or jacket, may comprise two layers of a synthetic material, such as a synthetic fleece, with a heating layer sandwiched between the two fleece layers. Alternatively, an item of heated clothing may comprise a soft inner or base layer, with an outer layer for protection from environmental elements, with the heating layer sandwich between the two layers.
In heated clothing, the heating layer typically comprises a heat element system connected to a heat source. There are several heating technologies employed for the heat element system including copper wire, nichrome wire, metal “mesh”, carbon-embedded fabric, and carbon fibers.
An electrical heat source is connected to the heat element system, for powering system. For example in heated clothing designed for use on vehicles such as motorcycles and snowmobiles, a 12 volt electrical connector for connecting the heated garment to the vehicle's battery is used. Some heated garments are provided with a well-known cigarette lighter plug, so that the garment can be plugged into the vehicle's cigarette lighter receptacle. A disadvantage of this type of heated clothing is that the wearer must be in close proximity to an external electrical power source.
For electrically powered heated clothing designed for use where no external power source is available, batteries, including rechargeable batteries, are used to power the heat source. A disadvantage of batteries, both rechargeable and non-rechargeable, is they have a very limited life span, typically only hours before the batteries must be either replaced with new batteries or recharged. A disadvantage of rechargeable batteries, such as nickel metal hydride or lithium batteries, is that their “battery memory” diminishes over time and reduces the battery's capability to recharge further reducing the useful hours of the battery. Also, there are health concerns about the electrical currents of electrically powered heated traveling in close proximity to the wearer's body and what effects those electrical currents may have on the wearer's body.